Aircraft refueling boom soft limits control

ABSTRACT

A control system for an aircraft refueling boom controls the movements of the boom in certain areas in a total field of movement volume of possible boom movements based on the location of the boom in the total field of movement volume and based on the current rate of movement of the boom in the total field of movement volume.

This application is a divisional application of application Ser. No.14/793,331, filed on Jul. 7, 2015, and currently pending.

This invention is made with Government support under Contract No,KC-46EMD FA8625-11-C-6600 awarded by the Department of Defense. Thegovernment has certain rights in this invention.

FIELD

This disclosure pertains to an aircraft refueling boom and the aspect ofits control system that controls the movement of the aircraft refuelingboom in certain areas in the total field of movement volume of possibleboom movements based on the location of the boom in the total volume ofpossible boom movements, the operator input to the control system andthe current rate of movement of the boom.

BACKGROUND

Aircraft refueling booms can be moved through a wide range of movementin response to operator input signals sent to the boom control system.The operator input signals are produced in response to manualmanipulation of an input device by the operator of the boom. Forexample, an aircraft refueling boom can be controlled to move through afield of movement of the boom by an operator manually manipulating ajoystick control device. The operator movement of the joystick forwardlyor rearwardly would cause the control system to move the boom downwardlyor upwardly, respectively. The operator movement of the joystick to theleft or to the right would cause the control system to move the boom tothe left or to the right, respectively.

The aircraft refueling boom field of movement through which the boom canbe moved in response to input by the operator is limited in order toavoid damage to the boom, damage to the aircraft being refueled, anddamage to the tanker aircraft from which the boom extends. For example,the aircraft refueling boom field of movement is limited by the softlimit control system of the boom to avoid the boom impacting with thefuselage of the tanker aircraft. Such an impact could damage the boom orthe refueling nozzle of the boom. Furthermore, such an impact couldresult in the boom damaging the fuselage of the tanker aircraft. Thus,aircraft refueling boom control systems that oppose certain controlsignals produced by an operator's manual movement of a control device toavoid damage to the boom, the refueling nozzle and the tanker aircraftfuselage are desirable.

SUMMARY

The aircraft refueling boom soft limits control system of thisdisclosure controls movements of an aircraft refueling boom in responseto control signals sent to the control system by an operator of theaircraft refueling boom. The control system controls the movements ofthe aircraft refueling boom within a total field of movement volumerelative to the tanker aircraft deploying the boom. The total field ofmovement volume is a general conical volume that is defined by thelength of the boom with the distal end of the boom being moved in acircle at the base of the conical volume and the proximal end of theboom connected to the tanker aircraft being at the apex of the conicalvolume. The total field of movement volume is surrounded by a movementlimit threshold. The movement limit threshold is like an imaginarypartition or wall that surrounds the total field of movement volume. Thecontrol system of the boom prevents the boom from crossing the movementlimit threshold. The total field of movement volume is well spaced fromthe tanker aircraft fuselage or other structures of the tanker aircraftto avoid any damage to the tanker aircraft or the tanker aircraftstructures resulting from the boom coming into contact with the tankeraircraft or the tanker aircraft structures.

The total field of movement volume has a central movement volume. In thecentral movement volume the movement of the boom is unrestricted. Thecentral movement volume is also a general conical volume that is definedby the length of the boom when the distal end of the boom is moved in acircle at the base of the central movement conical volume with theproximal end of the boom connected to the tanker aircraft being at theapex of the central movement conical volume. In the central movementvolume the control system of the boom controls the movements of the boomin response to the operator's manual movements of a control device, forexample a joystick. The control system does not impose any restrictionson the movements of the boom in response to the operator's movements ofthe joystick. In the central movement volume, the boom is free to moveto the left or right and upwardly or downwardly as viewed by theoperator of the boom in response to the control signals sent to thecontrol system by the operator's manual movements of the joystick. Thecentral movement volume is surrounded by a restricted movementthreshold. The restricted movement threshold defines the outer bounds ofthe central movement volume. The restricted movement threshold is likean imaginary conical partition or wall within the total field ofmovement volume that separates the central movement volume from theremainder of the total field of movement volume.

Surrounding the central movement volume and surrounding the restrictedmovement threshold is a restricted movement volume. The restrictedmovement volume is also a general hollowed conical volume that is largerthan and surrounds the central movement volume. The restricted movementvolume is positioned between the restricted movement threshold and themovement limit threshold. In the restricted movement volume, the controlsystem places some restrictions on the movements of the boom resultingfrom the operator's manual movements of the joystick. For example, asthe operator moves the joystick and sends input signals to the controlsystem to cause the control system to move the boom from the centralmovement volume, through the restricted movement threshold and into therestricted movement volume, the control system senses the movement ofthe boom across the restricted movement threshold. The control systemthen opposes the operator's movements of the joystick and reduces orrestricts the movement of the boom through the restricted movementvolume in the direction of the boom chosen by the manual input of theoperator.

Basically, the control system progressively slows down the movement ofthe boom through the restricted movement volume as the boom approachesthe movement limit threshold surrounding the total field of movementvolume. Should the operator continue to operate the joystick to controlmovement of the boom to the movement limit threshold, the control systemprevents further movement of the boom in the direction of the movementlimit threshold. In this way, the control system restricts the movementof the boom to contain the boom in the total field of movement volumewhere the boom is spaced well away from its mechanical limits, thetanker aircraft fuselage and/or a tanker aircraft structures, preventingpotential impact of the boom with the tanker aircraft fuselage orstructures.

In order to ensure that the control system prevents the boom from movingbeyond the total field of movement volume and potentially reaching theboom's mechanical limits, contacting the tanker aircraft fuselage orstructures of the tanker aircraft, the control system monitors the rateor speed at which the boom is controlled to move from the centralmovement volume, across the restricted movement threshold and into therestricted movement volume. By the control system monitoring the rate atwhich the boom moves from the central movement volume, through therestricted movement threshold and into the restricted movement volume,the control system can determine the force and amount of time requiredto overcome the inertia of the mass of the moving boom and controlstopping of the boom movement as the boom reaches the movement limitthreshold. For example, when the control system senses the boom movingat a first rate or speed of movement through the central movement volumeand into the restricted movement area, the control system controls theactuators of the boom movement to exert a first force against theinertia of the boom for a first period of time to ensure that themovement of the boom through the restricted movement volume stops beforethe boom reaches the movement limit threshold. When the control systemsenses the boom moving at a second rate or speed of movement through thecentral movement volume and into the restricted movement volume, and thesecond rate of movement is larger than the first rate of movement, thenthe control system controls the actuators of the boom movement to exerta second force that is larger than the first force against the inertiaof the boom movement for a second period of time to ensure that the boomstops moving through the restricted movement volume before the boomreaches the movement limit threshold.

By sensing the rate or speed of movement of the boom through the centralmovement volume, across the restricted movement threshold and into therestricted movement volume, the control system ensures that a sufficientstopping force will be exerted against the inertia of the boom movingthrough the restricted movement volume in sufficient time to stop themovement of the boom when the boom reaches the movement limit threshold.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments or may be combined in yetother embodiments, further details of which can be seen with referenceto the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of aircraft production and service methodology.

FIG. 2 is a block diagram of an aircraft.

FIG. 3 is a representation of a perspective view of an aircraftsupporting an aircraft refueling boom operated by the control system ofthis disclosure.

FIG. 4 is a representation of a block diagram of a manually operatedcontrol device and a control system that controls the movements of theaircraft refueling boom of this disclosure.

FIG. 5 is a representation of a diagram of the field of movement volumeof the aircraft refueling boom, the central movement volume of the boomand the restricted movement volume of the boom controlled by the controlsystem of this disclosure.

FIGS. 6-9 are representations of movement of the aircraft refueling boomthrough the field of movement volume in response to manual input to themanual control device where the boom movements are controlled by thecontrol system of this disclosure.

DETAILED DESCRIPTION

Referring more particularly to the drawings, embodiments of thedisclosure may be described in the context of an aircraft manufacturingand service method 10 as shown in FIG. 1 and an aircraft 12 as shown inFIG. 2. During pre-production, exemplary method 10 may includespecification and design 14 of the aircraft 12 and material procurement16. During production, component and subassembly manufacturing 18 andsystem integration 20 of the aircraft 12 takes place. Thereafter, theaircraft 12 may go through certification and delivery 22 in order to beplaced in service 24. While in service by a customer, the aircraft 12 isscheduled for routine maintenance and service 26 (which may also includemodification, reconfiguration, refurbishment, and so on).

Each of the processes of method 10 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof venders, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 2, the aircraft 12 produced by exemplary method 10 mayinclude an airframe 28 with a plurality of systems 30 and an interior32. Examples of high-level systems 30 include one or more of apropulsion system 34, an electrical system 36, a hydraulic system 38,and an environmental system 40. Any number of other systems may beincluded. Although an aerospace example is shown (aircraft, rockets),the principles of the invention may be applied to other industries, suchas the automotive, railroad or tooling industry.

Apparatus and methods embodied herein may be employed during any one ormore of the stages of the production and service method 10. For example,components or subassemblies corresponding to production process 18 maybe fabricated or manufactured in a manner similar to components orsubassemblies produced while the aircraft 12 is in service. Also, one ormore apparatus embodiments, method embodiments, or a combination thereofmay be utilized during the production stages 18 and 20, for example, bysubstantially expediting assembly of or reducing the cost of an aircraft12. Similarly, one or more of apparatus embodiments, method embodiments,or a combination thereof may be utilized while the aircraft 12 is inservice, for example and without limitation, to maintenance and service26.

This disclosure pertains to an aircraft refueling boom and its controlsystem that are similar to those disclosed in the international patentpublication No. WO 2012/030347, which is assigned to the assignee ofthis application and is incorporated herein by reference.

FIG. 3 is a representation of a tanker aircraft 42 having a refuelingboom 44. The movements of the refueling boom 44 are controlled by thesoft limits control system of this disclosure in response to controlsignals sent to the control system by an operator of the aircraftrefueling boom. The boom supports a nozzle 46 that communicates withfuel tanks (not shown) inside the tanker aircraft 42. The boom 44 andthe soft limits control system provide in-flight refueling to arefueling receiver 48 of a separate aircraft 50. The soft limits controlsystem controls the movements of the boom 44 in an upward or downwarddirection as viewed by the boom operator in the aircraft and representedby the arrow 52, a left or right direction as viewed by the boomoperator in the aircraft 42 and represented by the arrow 54, or acombination of these directions within a total field of movement volumerelative to the tanker aircraft 42 deploying the boom 44. The softlimits control system controls the operation of rudders and elevator 56on the boom 44 to move the boom 44 through the total field of movementvolume.

FIG. 4 is a representation of the soft limits control system 62 of thisdisclosure. As represented in FIG. 2, the soft limits control system 62controls movements of the boom 44 in response to input signals receivedfrom a manual control device, such as a joystick 64 that is manuallymanipulated by an operator of the boom inside the aircraft 42. Inresponse to the manual manipulation of the joystick 64, the soft limitscontrol system 62 controls the rudders to move the boom left or right asrepresented by the arrow 54, or the elevator to move the boom 44upwardly or downwardly along the arrow 52, or controls a combination ofthese movements.

During operation of the boom 44, situations can occur that areunexpected by the boom operator. Such situations can cause the boomoperator to make manual movements of the joystick 64 that result in boommovements that could be dangerous to the tanker aircraft 42 or therefueling receiver 48 of the separate aircraft 50 being refueled by thetanker aircraft. For example, the boom operator could make movements ofthe joystick 64 that result in the boom being moved to a mechanicallimit of the boom total field of movement where the boom has thepotential for causing damage to itself, contacting and causing damage tothe aircraft fuselage or a structure of the aircraft. The soft limitscontrol system 62 is programmed to control the movements of the boom 44in response to manual movements of the joystick 64 by the operator, andalso to control the movements of the boom 44 that override control inputsignals from the joystick 64 and restrict movements of the boom thatcould potentially cause damage to the aircraft 42 and/or structures ofthe aircraft.

In response to the operator of the boom 44 making manual movements ofthe joystick 64, an input control signal 68 is sent from the joystick 64to the soft limit control system 62. The input control signal 68 isreceived by a summing junction 70 of the soft limit control system 62.The summing junction 70 combines the input control signal 68 with asignal received from a feedback loop (to be described) and sends asignal to the boom control logic 72.

The boom control logic 72 includes fly by wire controller informationthat is used to determine a first control signal 74 that is output tothe actuators 76 of the rudders and elevator 56. The first controlsignal 74 controls the actuators 76 to position the rudders and elevator56 to control the up or down movements or left to right movements of theboom 44 desired.

The movement of the rudders and elevator cause the boom to move. Theboom motion is sensed by the boom position sensors and one or moreinertial measurement units.

The one or more inertial measurement unit sensors 82 generate a secondcontrol signal 84 as feedback to the boom control logic 72. The inertialmeasurement unit sensors 82 provide input regarding an actual angularrate and linear acceleration of movement of the boom 44.

Additionally, an output signal 80 from the boom dynamics 78 is providedto boom position sensors 86 which gather information on a position ofthe boom 44 relative to the aircraft 42. An output signal 88 from theboom position sensors 86 is also provided to imposed limits 92 whichinclude logic governing imposed limits applied to the boom 44. Forexample, the imposed limits 92 of the control system 62 define a centralmovement volume in which there is unrestricted operator control ofmovements of the boom 44, a restricted movement volume that surroundsthe central movement volume and in which the control system 62 imposessome restrictions on boom movements, and a movement limit threshold thatsurrounds the restricted movement volume and prevents further movementof the boom 44 beyond the movement limit threshold. An output signal 94of the imposed limits 92 is fed back to the summing junction 70 wherethe output signal 94 of the imposed limits 92 offsets or negates atleast a portion of the input control signal 68 generated by the boomoperators movements of the joystick 64.

As further described with reference to FIGS. 5-10, when the boom 44 isoperated in a central movement volume, the operator of the boom 44 maymove the boom with full control and no restrictions. The centralmovement volume is a general conical volume that is defined by thelength of the boom 44 when the distal end of the boom or nozzle 46 ismoved in a circle at the base of the central movement conical volumewith the proximal end of the boom 44 connected to the tanker aircraft 44being at an apex of the central movement conical volume. In the centralmovement volume, the boom is free to move to the left or right andupwardly or downwardly as viewed by the operator of the boom in responseto the input control signal 68 sent to the control system 62 by theoperator's manual movement of the joystick 64. The central movementvolume is surrounded by a restricted movement threshold. The restrictedmovement threshold defines the outer bounds of the central movementvolume. The restricted movement threshold is like an imaginary conicalpartition or wall that surrounds the central movement volume.Surrounding the central movement volume and surrounding the restrictedmovement threshold is a restricted movement volume. When the boom 44moves from the central movement volume, through the restricted movementthreshold and into the restricted movement volume, the output signal 94from the imposed limits 92 received at the summing junction 70 reducesor partially offsets the input control signal 68 so that a greater ormore pronounced operator input is required at the joystick 64 togenerate an input control signal 68 that may at least partially overcomethe output signal 94 of the imposed limits 92 at the summing junction70. When the boom 44 reaches the movement limit threshold that surroundsthe restricted movement volume, the output signal 94 from the imposedlimits 92 entirely offsets or blocks the input control signal 68. As aresult, no matter to what extent the operator of the boom 44 moves thejoystick 64 in the direction where the boom 44 has reached the movementlimit threshold, the output signal 94 from the imposed limits 92 appliedto the summing junction 70 cancels the control input signal 68.

FIG. 5 is a representation of a total field of movement of the boom 44relative to the aircraft 42 that is controlled by the control system 62.In FIG. 5, the total field of movement is represented by the solid line96. Although the total field of movement 96 is shown in two dimensionsin FIG. 5, it should be understood that the boom 44 and the nozzle 46 ofthe boom move in a three-dimensional volume. During refuelingoperations, the nozzle 46 of the boom 44 is moveable by the controlsystem 62 in the volume having the general configuration of a truncatedcone at the bottom of the total field of movement 96 shown in FIG. 5.The boom 44 moves through the volume having the general configuration ofa cylinder at the top of the total field of movement volume 96represented in FIG. 5. The solid line 96 represents a movement limitthreshold in the control logic of the control system 62. The movementlimit threshold 96 is like an imaginary partition or wall that surroundsthe total field of movement volume. The control system 62 controls themovement of the boom 44 and prevents the boom 44 from crossing themovement limit threshold 98. The total field of movement volume 96within the movement limit threshold 98 is well spaced from the tankeraircraft 42 to avoid any damage to the tanker aircraft 42 or tankeraircraft structures resulting from the boom 44 coming into contact withthe tanker aircraft or the tanker aircraft structures.

The total field of movement volume 96 has a first, central movementvolume 100. The central movement volume 100 is surrounded by arestricted movement threshold 102. The central movement volume 100within the restricted movement threshold 102 has a general configurationof a truncated cone that is defined by the length of the boom 44 whenthe distal end or nozzle 46 of the boom is moved in a circle at the baseof the truncated cone and with the proximal end of the boom connected tothe tanker aircraft 42 being at the apex. In the central movement volume100 defined by the restricted movement threshold 102, movement of theboom is unrestricted by the control system 62. In the central movementvolume 100, the control system 62 controls movements of the boom 44 inresponse to the operator's manual movements of the joystick 64. Thecontrol system 62 does not impose any restrictions on the movements ofthe boom 44 in response to the operator's movements of the joystick 64.In the central movement volume defined by the restricted movementthreshold 102, the boom 44 is free to move to the left or right andupwardly or downwardly as viewed by the operator of the boom in responseto the input control signals 68 sent to the control system 62 by theoperator's manual movements of the joystick 64. The restricted movementthreshold 102 defines the outer bounds of the central movement volume100. The restricted movement threshold 102 is like an imaginarypartition or wall within the movement limit threshold 98 that separatesthe central movement volume 100 from the remainder of the total field ofmovement volume 96 within the movement limit threshold 98.

Surrounding the central movement volume 100 is a second, restrictedmovement volume 104. The restricted movement volume 104 is positionedoutside of the central movement volume 100 and surrounds the centralmovement volume 100 and the restricted movement threshold 102. Therestricted movement volume 104 extends from the restricted movementthreshold 102 to the movement limit threshold 98. The restrictedmovement volume 104 is also a general hollowed conical volume that islarger than and surrounds the central movement volume 100 and therestricted movement threshold 102. In the restricted movement volume104, the control system 62 puts some restrictions on the movements ofthe boom 44 resulting from the operator's manual movements of thejoystick 64.

FIGS. 6-9 are representations of the movement of the aircraft refuelingboom 44 through the total field of movement volume 96 in response tomanual input to the joystick 64 where the boom movements are controlledby the control system 62.

FIG. 6 is a representation of a first situation in which the boom 44 ispositioned in the central movement volume 100 within the restrictedmovement threshold 102. In the central movement volume 100, movement ofthe boom 44 is unrestricted by the control system 62. The boom 44, theposition of which is being monitored by the control system 62, is at afirst position within the central movement volume 106. The joystick 64is not subject to any control input from the operator. Because nocontrol input is applied by the operator to the joystick 64, the boom 44remains at its current position represented in FIG. 6.

FIG. 7 is a representation of a second situation in which the boomoperator moves the joystick 64 forwardly, sending an input controlsignal 68 to the control system 62. In response to the forward movementof the joystick 64, the boom 44 moves downwardly in the central movementvolume 100 to a second position below the first position of the boom 44represented in FIG. 6. Because the position of the boom 44 representedin FIG. 7 is still in the central movement volume 100 where movement ofthe boom is unrestricted by the control system 62, the control system 62fully implements the movement of the boom 44 in response to the inputcontrol signal 68 received from the joystick 64.

FIG. 8 is a representation of further downward movement of the boom 44in the central movement volume 100 resulting from the continued presenceof the joystick 64 in its pushed forward position. As represented inFIG. 8, the boom 44 has been moved from its first position representedin FIG. 6 to a third position within the central movement volume 100adjacent the restricted movement threshold 102. Because the inputcontrol signal 68 produced by the pushed forward position of thejoystick 64 continues to be applied to the control system 62, the boom44 continues to move downwardly in response to the input control signal68 at a same rate within the central movement volume 100. Because theboom 44 continues to be moved in the central movement volume 100, theinput control signal 68 resulting from the pushed forward position ofthe joystick 64 is fully implemented without any reduction in responsefrom the control system 62.

FIG. 9 is a representation of movement of the boom 44 to a fourthposition. A continued positioning of the joystick 64 in the pushedforward position by the boom operator directs the boom 44 to move in thesame direction of movement as represented in FIGS. 7 and 8 with the boom44 moving through the restricted movement threshold 102 and through therestricted movement volume 104 toward the movement limit threshold 98.

In response to the boom 44 moving through the restricted movementthreshold 102 and into the restricted movement volume 104, the controlsystem 62 reduces the response of the boom 44 to the pushed forwardposition of the joystick 64 by the boom operator. Thus, if the boomoperator's pushed forward positioning of the joystick 64 is continued,the control system 62 controls the boom 44 to respond more slowly. Ifthe boom operator wishes to move the boom 44 in the same direction atthe same rate, the operator must increase a magnitude of the manualinput to the joystick 64 and push the joystick further forward.

The control system 62 progressively slows down the movement of the boom44 through the restricted movement volume 104 as the boom 44 approachesthe movement limit threshold 98 surrounding the total field of movementvolume 96. Should the boom operator continue to operate the joystick 64to control movement of the boom 44 to the movement limit threshold 98,the control system 62 takes over complete control of the boom 44 andstops the movement of the boom at the movement limit threshold 98. Inthis way, the soft limits control system 62 restricts the movement ofthe boom 44 to contain the boom in the total field of movement volume 96where the boom is spaced well away from its mechanical limits, thetanker aircraft fuselage and/or a tanker aircraft structure, preventingpotential impact of the boom 44 with the tanker aircraft fuselage orstructure.

In order to insure that the control system 62 prevents the boom 44 frommoving beyond the total field of movement volume and potentiallyreaching its mechanical limits, contacting the tanker aircraft 42 orstructures of the tanker aircraft, the control system 62 monitors boththe position of the boom 44 in the total field of movement volume 96 andthe rate or speed of movement at which the boom 44 is controlled to movefrom the central movement volume 100, across the restricted movementthreshold 102 and into the restricted movement volume 104. By thecontrol system 62 monitoring the position of the boom 44 in the totalfield of movement volume 96 and the rate at which the boom moves fromthe central movement volume 100, through the restricted movementthreshold 102 and into the restricted movement volume 104, the controlsystem 62 can determine the force and amount of time required toovercome the inertia of the mass of the moving boom 44 and controlstopping of the boom movement as the boom 44 reaches the movement limitthreshold 98. For example, when the control system 62 senses the boom 44moving at a first rate or speed of movement through the central movementvolume 100, across the restricted movement threshold 102 and into therestricted movement volume 104, the control system 62 controls theactuators 76 to move the rudders and elevator 56 to positions relativeto the boom 44 where the rudders and elevator 56 exert a first forceagainst the inertia of the boom 44 for a first period of time to ensurethat the movement of the boom 44 through the restricted movement volume104 stops before the boom reaches the movement limit threshold 98. Whenthe control system 62 senses the boom moving at a second rate or speedof movement through the central movement volume 100, through therestricted movement threshold 102 and into the restricted movementvolume 104 where the second rate or speed of movement is greater thanthe first rate or speed of movement, the control system 62 controls theactuators 76 to move the rudders and elevator 56 to positions relativeto the boom 44 where the rudders and elevator 56 exert a second forcethat is larger than the first force against the inertia of the boommovement for a second period of time to ensure that the boom 44 stopsmoving through the restricted movement volume 104 before the boomreaches the movement limit threshold 98.

By sensing both the position of the boom 44 in the total field ofmovement volume 96 and the rate or speed of movement of the boom throughthe central movement volume 100, across the restricted movementthreshold 102 and into the restricted movement volume 104, the controlsystem 62 ensures that a sufficient stopping force in sufficient timewill be exerted against the inertia of the boom moving through therestricted movement volume 104 to stop the movement of the boom 44 whenthe boom reaches the movement limit threshold 98.

Although the operation of the boom soft limits 62 controlling the rateof movement of the boom 44 has been described above with reference toFIGS. 6-9 for downward movement of the boom through the total field ofmovement volume 96, it should be understood that the boom soft limits 62control left and right movements of the boom 44, upward and downwardmovements of the boom 44 and combinations of these movements through thetotal field of movement volume 96 in the same manner.

As various modifications could be made in the construction of theaircraft refueling boom soft limits control and its method of operationherein described and illustrated without departing from the scope of theinvention, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting. Thus, the breadth and scope of thepresent disclosure should not be limited by any of the above describedexemplary embodiments, but should be defined only in accordance with thefollowing claims appended hereto and their equivalents.

The invention claimed is:
 1. A method of insuring safe movements of arefueling boom comprising: controlling movements of the refueling boomin a central movement volume relative to the refueling boom and in arestricted movement volume relative to the refueling boom where therestricted movement volume extends around the central movement volumeand preventing movements of the boom past a movement limit thresholdthat extends around the restricted movement volume; sensing a positionof the refueling boom in the central movement volume and sensing a rateof movement of the refueling boom in the central movement volume;sensing a position of the refueling boom in the restricted movementvolume and sensing a rate of movement of the refueling boom in therestricted movement volume; controlling movements of the refueling boomin response to only control signals when the position of the refuelingboom is sensed in the central movement volume; and, limiting movementsof the refueling boom in the restricted movement volume in the responseto the sensed rate of movement of the refueling boom in the restrictedmovement volume and preventing movement of the refueling boom past themovement limit threshold.
 2. The method of claim 1, further comprising:moving the boom in a first manner in response to sensing a first rate ofmovement of the boom; and, moving the boom in a second manner inresponse to sensing a second rate of movement of the boom.
 3. The methodof claim 2, further comprising: the first manner being different fromthe second manner; and, the first rate of movement being different fromthe second rate of movement.
 4. A method of insuring safe movements of arefueling boom comprising: controlling movements of the refueling boomin a central movement volume relative to the refueling boom; controllingmovements of the refueling boom in a restricted movement volume relativeto the refueling boom where the restricted movement volume extendsaround the central movement volume; sensing a position of the refuelingboom in the central movement volume; sensing a position of the refuelingboom in the restricted movement volume; controlling movements of therefueling boom in response to only input control signals when theposition of the refueling boom is sensed in the central movement volume;and, controlling movements of the refueling boom in response to inputcontrol signals and feedback output signals when the position of therefueling boom is sensed in the restricted movement volume.
 5. Themethod of claim 4, further comprising: having no restrictions onmovements of the refueling boom when the position of the refueling boomis sensed in the central movement volume; and, having restrictions onthe movements of the refueling boom when the position of the refuelingboom is sensed in the restricted movement volume.
 6. The method of claim4, further comprising: having no restrictions on a rate of movement ofthe refueling boom when the position of the refueling boom is sensed inthe central movement volume; and, having restrictions on the rate ofmovement of the refueling boom when the position of the refueling boomis sensed in the restricted movement volume.
 7. The method of claim 4,further comprising: preventing movement of the refueling boom beyond amovement limit threshold that surrounds the restricted movement volume.8. The method of claim 7, further comprising: limiting movements of therefueling boom to movements inside the movement limit threshold.
 9. Themethod of claim 4, further comprising: controlling movements of therefueling boom with the refueling boom attached to a tanker aircraft.10. The method of claim 4, further comprising: the central movementvolume having a conical configuration.
 11. The method of claim 4,further comprising controlling movement of the refueling boom inresponse to the input control signals that are produced by manualmanipulation of a manual control device.
 12. The method of claim 11,further comprising the manual control device being a joystick.
 13. Amethod of insuring safe movements of a refueling boom comprisingcontrolling movements of the refueling boom in a total field of movementvolume, the total field of movement volume comprising a first volume anda second volume; sensing a position of the refueling boom in the firstvolume when the refueling boom is positioned in the first volume;sensing a position of the refueling boom in the second volume when therefueling boom is positioned in the second volume; controlling movementof the refueling boom in response to only input control signals when theposition of the refueling boom is sensed in the first volume; and,controlling movement of the refueling boom in response to input controlsignals and in response to a feedback output signal when the position ofthe refueling boom is sensed in the second volume.
 14. The method ofclaim 13, further comprising having no restrictions on movements of therefueling boom when the position of the refueling boom is sensed in thefirst volume; and, having restrictions on the movements of the refuelingboom when the position of the refueling boom is sensed in the secondvolume.
 15. The method of claim 13, further comprising having norestrictions on a rate of movement of the refueling boom when theposition of the refueling boom is sensed in the first volume; and,having restrictions on the rate of movement of the refueling boom whenthe position of the refueling boom is sensed in the second volume. 16.The method of claim 13, further comprising preventing movements of therefueling boom beyond a movement limit threshold that surrounds thesecond volume.
 17. The method of claim 13, further comprising: the firstvolume being separate from the second volume.
 18. The method of claim13, further comprising: limiting movement of the refueling boom toinside the total field of movement volume.
 19. The method of claim 13,further comprising: controlling movement of the refueling boom from atanker aircraft.
 20. The method of claim 19, further comprising:controlling movement of the refueling boom by controlling movement oftwo rudders on the refueling boom and controlling movement of anelevator on the refueling boom.